Transparent tablet for evaluation of motor responses

ABSTRACT

Transparent tablet for evaluation of motor responses furnishing the coordinates of the contact points of at least one conductive probe tip on said tablet, the latter being overlaid on its outer face by a resistive transparent film, such as tin dioxide, and by the provision of current-generating means in a first and in a second directions, setting up voltage gradients along said resistive transparent film in said first and second directions. The voltages picked up by said conductive probe tip at the point of contact are proportional to the distance of said point to the edges of the tablet along each of said directions, the numerical values of said point coordinates being furnished by the conversion to digital form, by an A/D converter, of said voltage.

BACKGROUND OF THE INVENTION

[0001] The present invention refers to a device that furnishes the spatial and temporal coordinates of the points of the point in a transparent plate that is touched by the tip of a probe. Such a device is particularly useful in the evaluation of motor prerformance, alternative or augmented communication systems, map-making, support systems for special teaching techniques, etc.

[0002] The integration between several sources of sensory information and the production of motor responses is a physiological function required in many common situations, with applications in the research of motor behavior in normal and handicapped individuals.

[0003] One line of research of said function is based on the touch, with probe tips, of targets of different shapes, dimensions, distances and positions, said targets being either static or dynamic. Static targets comprise figures printed or drawn in sheets of paper or cardboard, while dynamic targets can be shown in video monitors or projection devices. The act of touching can be triggered by visual or auditory stimuli, so as to allow the detection of correlations between the subject's responses to standardized stimuli. Said investigations are carried out having in mind the clinical analysis and remedial action in dysfunction-bearing populations. However, said research has been hindered by the lack of available specific and sophisticated tools that—owing to their high cost—are seldom available in areas with poor socio-economic conditions.

[0004] In view of the preceding, the invention has the main objective of providing a low-cost device that can be employed either with static or dynamic targets, and suitable for connection to a personal computer.

SUMMARY OF THE INVENTION

[0005] The above object is achieved by the invention by means of a device comprising a transparent glass plate overlaid on its outer surface by a transparent resistive film provided with means that produce sheet electric currents in a first and in a second directions, said currents having attributes that allow the identification of said currents, as well as at least one conductive probe, the determination of the coordinates of the point of contact between the tip of said probe and said surface being achieved by the measurement of the voltages picked up by said tip in each of said directions, said voltage values being digitized by an analogic/digital converter.

[0006] According to the invention, said identifying attributes are provided by the multiplexation of said currents.

[0007] According to another feature of the invention, the identification of the currents in a first direction and in a second direction is provided by the time switching of said currents, this is to say, the currents are applied to the transparent resistive sheet alternately and sequentially in a first and in a second directions.

[0008] According to another feature of the invention, the first current is an AC current with a first frequency and the second current is an AC current with a second frequency, aid first and second currents being simultaneously applied to said transparent sheet.

[0009] According to yet another feature of the invention, said glass plate has a rectangular shape and said directions are ortogonal to each other.

[0010] The above mentioned features of the invention shall be better understood by the following description of several illustrative embodiments that follow, taken in connection to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 shows, by means of a block diagram, the main component parts of the proposed invention.

[0012]FIG. 2 shows the electrical connections relating to the transparent resistive film that overlays the glass plate.

[0013]FIG. 3 shows the block diagram of a system provided with two probes, according to the invention.

[0014]FIG. 4 shows a second embodiment of the invention.

[0015]FIG. 5 shows the structure of the data packets forwarded to the computer, corresponding to one- and two-probe devices.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Referring now to the drawing of FIG. 1, the object of the invention consists of a tablet comprising a glass plate 10 overlaid wit a transparent resistive film such as tin dioxide, and at least on conducting probe 21 connected by a flexible cable 22 to the A/D converter 24, the output of which is connected to a microprocessor 20 which processes the information collected by the probe tip. Said processing performed by block 27 comprises formatting the information concerning the X and Y coordinates at the moment that said tip touched the tablet. Said processing additionally comprises the filtering of transients and noise, as well as repeated or null readings, which can be implemented by software stored in microprocessor 20.

[0017] The data is formatted according to the application, because the system allows the emulation of a standard mouse, among other features. In this case the rate of transmission is 1200 bauds, the mouse function being activated by means of double press and drag, for example. In another embodiment, the probe operates as a mouse, in which case it will be provided with a pushbutton which will be connected to the microprocessor input through a second wire.

[0018] When the application requires the X/Y position data in real-time, the transmitted packet comprises a start byte 61, two bytes 62, 63 containing the X value, one separating byte 64 and two bytes 65, 66 for the Y coordinate, such as depicted in FIG. 3-a. When two probes are used, an additional byte 67 is included, informing which probe the data refers to, followed by a separation byte 68, as shown in FIG. 3-b.

[0019] These packets are processed by the data communication block 28, which may be a USART or UART operating in the duplex mode, that communicates with the microcomputer by means of a serial interface 29 and 9-way cable, infrared or radio link, etc.

[0020] According to FIG. 2, the tablet comprises a rectangular glass plate overlaid with a resistive conducting transparent film such as, for example, tin dioxide, having a surface resistance in the order of 300 . . . 1000 ohms per square, in the embodiment described herein. According to the invention, a DC voltage is applied between vertical edges 21, 22 of the resistive film and, in the following half-cycle, the same voltage is applied between horizontal edges 26, 27. This operation is carried out by driver block 25, that generates two symmetrical square waves 28 and 29 with opposing phases, the former being forwarded by line 25 a to a first and second set of parallel-connected diodes, said first set comprising diodes 41 having their cathodes connected to upper edge 26 of said rectangular resistive film and said second set comprising diodes 24 having their anodes connected to the right-hand edge 22 of said rectangular resistive Mm. Opposed-polarity square wave 29 is forwarded to a third and fourth diode sets through line 25 b, said third diode set comprising diodes 42 having their anodes connected to lower edge 27 of said rectangular resistive film and the fourth diode set comprising diodes 23 having their cathodes connected to the left-hand edge of said rectangular resistive film. All diodes are uniformly distributed along the edges to which they are connected, the distance between them determining the precision of the measured touch-point coordinates.

[0021] According to the invention, when a voltage difference is applied between opposing edges, a laminar current is set up between said edges, the magnitude of which depends on the value of said voltage as well as on the film resistance. Considering, for instance, the half-period t₂-t₃ when wave 28 is negative and wave 29 is positive, diode sets 23 and 24 are directly polarized and conducting, while diode sets 41 and 42 are inversely polarized and cut-off. In this case, left-hand edge 21 of the tablet has a positive potential relative to right-hand edge 22, and current lines 43 are set between said edges. Therefore, the voltage measured at any point along the X direction will be in proportion to the distance of said point to said edges: right on the left-hand edge 21 the voltage value will be equal to 29′—which is the square-wave voltage 29 less the conduction voltage drop through the diodes. On the right-hand edge 22 the voltage will be equal to 29′, while in-between, it will have an intermediate magnitude. Each time the probe tip touches the tablet surface, the voltage at the contact point is read by the A/D converter 24.

[0022] In the following half-cycle t₃-t₄, the polarities of said square-waves are inverted, and diode sets 41 and 42 will conduct, the resulting current flux being directed from upper edge 26 to the lower edge, the voltage measured at each point of the tablet surface being proportional to the distance of said point to said edges.

[0023] According to FIGS. 1 and 2, microcontroller 20 is provided with an internal clock 26 which synchronizes operation of driver 25 as well as of A/D converter 24. The square-wave frequency is matched to the operating speed of said A/D converter, typically in the order of 1 kHz. When two probes are used, said clock also synchronizes the switching between readings, the X and Y coordinates of the first probe followed by the X and Y coordinates of the second probe.

[0024] The probe tips can be metal or a non-metallic conducting material. Soft or flexible conducting materials, such as graphite, are desirable due to reduction of friction against the conducting film surface and diminishing wear of the latter. The tip size determines the resolution in X and Y coordinate measurement, which is usually in the order of 1 millimetre.

[0025] A second embodiment of the invention is shown in FIG. 4. Instead of switching a DC voltage, two AC signals are simultaneously applied between opposing edges of the tablet. A first signal with frequency f₁, supplied by generator 53, is applied between the upper and lower edges while a second signal having frequency f₂, supplied by generator 54, is applied between the side edges. Therefore, two sets of current lines will coexist in said resistive film: a first set in the X direction with frequency f₁, and a second set of current lines in the Y direction with frequency f₁.

[0026] When probe tip 21 touched the resistive film surface, cable 22 will transmit a signal with two frequencies; the same will happen with probe tip 51 and cable 52. Said cables are connected to the two inputs of a switching device 25, which is controlled by the microprocessor clock 26, said switching device transmitting the signals picked up by probe tip 21 interspersed with the signals picked up by probe tip 51 to its output port. Said signals are fed to pass-band filters 55 and 58, respectively tuned to frequencies f₁ (correspondent to the X axis) and f₂ (correspondent to the Y axis), the rectification and filtering of said signals by blocks 56 and 57 furnishing DC voltages which are proportional to the position of each probe tip along the X and Y axes. A second switching device forwards, in alternation, said voltages to the A/D converter 24, the remaining processing of the information following the steps already described.

[0027] Although the preceding description was based in two illustrative embodiments, it will be understood that modifications can be introduced while remaining within the bounds of the invention. For instance, a different material can be substituted for the tin dioxide in the transparent film that overlays the glass plate, as long as this material exhibits the necessary features of transparency and uniformity.

[0028] Considering that the tablet of the invention is transparent, it can be employed in a large variety of applications, ranging from digitizing table, spatial keyboard, signature digitalization, mouse, and so on.

[0029] Therefore, the invention is defined by the following claims. 

1. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES furnishing the coordinates of the contact points of at least one conductive probe tip on a plate, wherein said plate is transparent and overlaid on its outer face by a resistive transparent film, and by the provision of means setting up electric currents in a first and in a second directions along said film, the distinction between said currents being provided by identifying features specific to each of said currents.
 2. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 1, wherein said identifying features consist of the timing of said currents provided by the alternate switching-on of the currents in said first and second directions.
 3. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 2, wherein the coordinates of said contact points are determinate by the measurement of the magnitudes of the voltages picked up by said probe tip when touching said resistive transparent film, in each of the two said directions.
 4. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 1, wherein said current identifying features consist of two different frequencies, each frequency being associated with the current in one of said two directions, and by the fact that the alternating voltages picked up by the probe tip are forwarded to bandeaus filters tuned to a first and a second said frequencies, followed by rectification and filtering of the resulting DC voltages.
 5. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 4, wherein the values of the DC voltages are digitized by an A/D converter.
 6. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 1, wherein said plate has a rectangular shape, the current lines being parallel to the X and Y axes, respectively.
 7. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claims 6, wherein said currents in a first and a second directions are provided by applying a DC voltage between the left-hand and the right-hand vertical edges of said tablet in a first half-cycle, and of a DC voltage between the upper and lower edges of the tablet in the second half-cycle, the operation of the A/D converter being synchronized with said first and second half-cycles.
 8. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 1, wherein two probes are provided, the voltages picked up by them being alternately monitored.
 9. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 8, wherein the transparent resistive film consists of tin dioxide.
 10. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 4, wherein the values of the DC voltages are digitized by an A/D converter.
 11. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 6, wherein said currents in a first and a second directions are provided by applying a DC voltage between the left-hand and the right-hand vertical edges of said tablet in a first half-cycle, and of a DC voltage between the upper and lower edges of the tablet in the second half-cycle, the operation of the A/D converter being synchronized with said first and second half-cycles.
 12. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 2, wherein said currents in the first and second directions are provided by applying a DC voltage between left-hand and right-hand vertical edges of said tablet in a first half-cycle, and applying a DC voltage between upper and lower edges of the tablet in a second half-cycle, the operation of the A/D converter being synchronized with said first and second half-cycles.
 13. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 7, wherein the transparent resistive film consists of tin dioxide.
 14. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 6, wherein the transparent resistive film consists of tin dioxide.
 15. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 5, wherein the transparent resistive film consists of tin dioxide.
 16. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 4, wherein the transparent resistive film consists of tin dioxide.
 17. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 3, wherein the transparent resistive film consists of tin dioxide.
 18. TRANSPARENT TABLET FOR EVALUATION OF MOTOR RESPONSES as claimed in claim 2, wherein the transparent resistive film consists of tin dioxide. 